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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Little-known microbes could help predict climate tipping points    
      
     Date:   
         June 1, 2023   
     Source:   
         Duke University   
     Summary:   
         Rising temperatures could push ocean plankton and other   
         single-celled creatures toward a carbon tipping point that fuels   
         more warming. The carbon-eaters could become carbon-emitters. But   
         new research shows it's also possible to detect early distress   
         signals before they get there.   
      
      
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   FULL STORY   
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   Researchers studying a group of widespread but often overlooked microbes   
   have identified a climate feedback loop that could accelerate climate   
   change. But it's not all bad news: this one comes with an early warning   
   signal.   
      
   Using a computer simulation, a team of scientists from Duke University   
   and the University of California, Santa Barbara, showed that most of the   
   world's ocean plankton and many other single-celled creatures in lakes,   
   peatlands and other ecosystems could cross a threshold where instead of   
   soaking up carbon dioxide, they start doing the opposite. That's because   
   of how warming affects their metabolism.   
      
   Because carbon dioxide is a greenhouse gas, that in turn could drive   
   up temperatures further -- a positive feedback loop that could lead to   
   runaway change, where small amounts of warming have an outsized impact.   
      
   But by carefully monitoring the abundances of these organisms, we might be   
   able to anticipate the tipping point before it gets here, the researchers   
   report in a study published June 1 in the journal Functional Ecology.   
      
   In the new study, researchers focused on a group of tiny organisms called   
   mixotrophs, so named because they mix up two modes of metabolism: they   
   can photosynthesize like a plant or hunt food like an animal, depending   
   on conditions.   
      
   "They're like the Venus fly traps of the microbial world," said first   
   author Daniel Wieczynski, a postdoctoral associate at Duke.   
      
   During photosynthesis, they soak up carbon dioxide, a heat-trapping   
   greenhouse gas. And when they eat, they release carbon dioxide. These   
   versatile organisms aren't considered in most models of global warming,   
   yet they play an important role in regulating climate, said senior author   
   Jean P. Gibert of Duke.   
      
   Most of the plankton in the ocean -- things like diatoms, dinoflagellates   
   - - are mixotrophs. They're also common in lakes, peatlands, in damp   
   soils and beneath fallen leaves.   
      
   "If you were to go to the nearest pond or lake and scoop a cup of water   
   and put it under a microscope, you'd likely find thousands or even   
   millions of mixotrophic microbes swimming around," Wieczynski said.   
      
   "Because mixotrophs can both capture and emit carbon dioxide, they're   
   like 'switches' that could either help reduce climate change or make   
   it worse," said co-author Holly Moeller, an assistant professor at the   
   University of California, Santa Barbara.   
      
   To understand how these impacts might scale up, the researchers developed   
   a mathematical model to predict how mixotrophs might shift between   
   different modes of metabolism as the climate continues to warm.   
      
   The researchers ran their models using a 4-degree span of temperatures,   
   from 19 to 23 degrees Celsius (66-73 degrees Fahrenheit). Global   
   temperatures are likely to surge 1.5 degrees Celsius above pre-industrial   
   levels within the next five years, and are on pace to breach 2 to 4   
   degrees before the end of this century.   
      
   The analysis showed that the warmer it gets, the more mixotrophs rely on   
   eating food rather than making their own via photosynthesis. As they do,   
   they shift the balance between carbon in and carbon out.   
      
   The models suggest that, eventually, we could see these microbes reach   
   a tipping point -- a threshold beyond which they suddenly flip from   
   carbon sink to carbon source, having a net warming effect instead of a   
   cooling one.   
      
   This tipping point is hard to undo. Once they cross that threshold,   
   it would take significant cooling -- more than one degree Celsius --   
   to restore their cooling effects, the findings suggest.   
      
   But it's not all bad news, the researchers said. Their results also   
   suggest that it may be possible to spot these shifts in advance, if we   
   watch out for changes in mixotroph abundance over time.   
      
   "Right before a tipping point, their abundances suddenly start to   
   fluctuate wildly," Wieczynski said. "If you went out in nature and   
   you saw a sudden change from relatively steady abundances to rapid   
   fluctuations, you would know it's coming."  Whether the early warning   
   signal is detectable, however, may depend on another key factor revealed   
   by the study: nutrient pollution.   
      
   Discharges from wastewater treatment facilities and runoff from farms and   
   lawns laced with chemical fertilizers and animal waste can send nutrients   
   like nitrate and phosphate into lakes and streams and coastal waters.   
      
   When Wieczynski and his colleagues included higher amounts of such   
   nutrients in their models, they found that the range of temperatures over   
   which the telltale fluctuations occur starts to shrink until eventually   
   the signal disappears and the tipping point arrives with no apparent   
   warning.   
      
   The predictions of the model still need to be verified with real-world   
   observations, but they "highlight the value of investing in early   
   detection," Moeller said.   
      
   "Tipping points can be short-lived, and thus hard to catch," Gibert   
   said. "This paper provides us with a search image, something to look   
   out for, and makes those tipping points -- as fleeting as they may be --   
   more likely to be found."  This research was supported by grants from the   
   Simons Foundation (689265), the National Science Foundation (1851194),   
   and the U.S. Department of Energy (DE- SC0020362).   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Global_Warming # Climate # Environmental_Issues #   
                   Weather   
             o Science_&_Society   
                   # Environmental_Policies # Resource_Shortage #   
                   World_Development # Ocean_Policy   
       * RELATED_TERMS   
             o Carbon_cycle o Carbon_dioxide_sink o Carbon_dioxide o   
             Fossil_fuel o Forest o Ocean_acidification o Carbon_monoxide   
             o Activated_carbon   
      
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   Story Source: Materials provided by Duke_University. Original written   
   by RA Smith. Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Daniel J. Wieczynski, Holly V. Moeller, Jean P. Gibert. Mixotrophic   
         microbes create carbon tipping points under warming. Functional   
         Ecology, 2023; DOI: 10.1111/1365-2435.14350   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230601160229.htm   
      
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